This invention relates to apparatus for actuating a plurality of electrical spring probes and a loaded planar test member into electrical contact.
Circuit board analysers are generally known employing an actuator assembly for relatively moving a plurality of electrical spring probes and a circuit board, bearing test points, into electrical contact.
One class of actuator assemblies actuates a bare board and the electrical spring probes into contact. A bare board is a circuit board, for example a printed circuit board, which does not have components loaded on the board. This bare board class of actuator assemblies generally utilizes a backing on the opposite side of the board from the electrical spring probes which keeps the board generally planar so that it makes electrical contact with all of the electrical spring probes and forms one wall of a vacuum chamber. An example of this bare board class of actuator assemblies is disclosed in co-pending application U.S. Ser. No. 851,847, now U.S. Pat. No. 4,138,186, filed Nov. 16, 1977. The co-pending patent application discloses a test apparatus for a bare planar test member. Included is a test member support plate. A movably mounted door plate provides access to a test location on the support plate. A resilient seal is mounted on the door plate and extends in sealing relation between the door plate and the support plate around the perimeter of the test location when the door plate is closed so as to form a resilient mounting for the door plate on the support plate. The sealing relation between the seal and the support plate is broken when the door plate is opened. A substantially sealed cavity includes the test location and comprises the support plate, the door plate and the seal. A plurality of probes are mounted on and extend through the support plate and each comprises a resiliently biased probe head exposed in the cavity. Ports for vacuum extend through the support plate to the vacuum chamber.
Such a device is not suitable for testing of loaded boards. Loaded boards are, for example, printed circuit boards which have components such as resistors, capacitors, etc., mounted on one side of the board. Since the loaded board must be inserted between the door plate and the test member support plate, the components prevent the door plate from making cntact with the surface of the printed circuit board.
Another class of actuator assemblies and the one to which the present invention is directed actuates a loaded board and electrical spring probes into contact. Loaded board actuable assemblies differ from the bare board class discussed above in that a backing cannot be used on the opposite side of the loaded board from the probes because of the components mounted on the board.
An example of a loaded board actuator assembly is disclosed in U.S. Pat. No. 4,017,793. The '793 patent discloses a printed circuit board tester which has an elastomeric member on which a loaded printed circuit board is positioned. The circuit board is supported on the elastomeric member by a thin nonconductive sealing foam sheet that has a cutaway central portion to permit the circuit board to makecontact with leads which extend through openings in the elastomeric member. The elastomeric member is in turn mounted on a rigid fiber glass plate or sheet which is positioned in opposed relation to a base member in which the leads are mounted. A diaphragm extends across the surface of the rigid fiber glass sheet on the opposite side from the base support and extends outwardly beyond the edges of the fiber glass sheet to the base member, thereby providing a vacuum chamber between the fiber glass sheet and the base member. A rectangular picture frame shaped molded fiber glass retainer extends over the edges of the elastomeric diaphragm and sealingly secures the perimeter of the diaphragm to the base member. Coil compression springs urge the fiber glass sheet away from the base until the elastomeric member is stopped against an inner edge of the retainer. A rectangular opening in the center of the retainer provides access for the loaded printed circuit board. Additionally, spacers are provided between the fiber glass sheet and the base. Evacuation of the vacuum chamber causes the fiber glass sheet and the printed circuit board to be drawn down against the leads. Such an arrangement is rather costly to manufacture due to the number of parts and the required assembly process.
Other loaded board actuator assemblies are also known. Some of these devices require that the printed circuit board be fixed and that the base support for the spring probes be moved upwardly to bring the spring probes into contact with the loaded printed circuit board under test.